How much lift for doubles wing?

[Guy Alcala]

It took me a few minutes to parse at first, but I think Guy is saying that he IS neutrally buoyant at the end of the dive (in the OP, he says -24lb of ballast at the end of the dive, which is about equal to and offset by the buoyancy of the drysuit), but much of that weight is from the tanks themselves (non-ditchable, non-distributable).

Right. In my current suit/undergarment (wicking layer plus single-layer fleece under a CF200) I'm +18, but using a White's Mk.3 two weekends back 4 more lb. of lead wasn't enough to get me neutral at the end of the dive. Depending on which undergarment I upgrade to I'm figuring I'll need 4-6 lb. more, or 22-24 lb. total with 500 PSI. And that agrees with most people's calculations for the buoyancy of their drysuit/undergarment combo.

I also need to be able to float my rig at the surface at the start of the dive. While I could normally count on some lift from the D.S., virtually all of my boat diving to date has been from an RIB. Because of tight space and the limited number of flat, hard surfaces, some or all of the rigs tend to get put overboard on tag lines and gearing up is finished in the water. While I usually can don singles in the boat if it's not moving too much, doubles would likely be very difficult to impossible, so I need enough lift from the wing to float the rig by itself. With no ditchable weight and assuming double HP100s @ ~ 15 lb. of gas, that means I need at least 39 lb. of lift at the start of the dive to float the rig.

Using less negative tanks than my Asahis to give me some ditchable/trimmable weight will definitely help, but I'm one of those people who was born sans hips, and although ensuing decades have added some padding, I have serious doubts about my ability to retain a separate weight belt. Even if it's put on under the crotch strap, you've still got a chance of losing it completely. Since unintentionally losing your weights is generally considered a really bad idea during a deco dive, I may have to use weight pockets on the waistbelt for doubles, although I need to experiment some more.

Guy

 

[Joakim Linde]

I also need to be able to float my rig at the surface...

Now it starts to make sense to me. Thanks for clarifying. So, I have two more questions then, if you don't mind:

a) How much lift do you think you need if you removed the requirement that the rig needs to float by itself on the surface?

b) How much lift does the rig need to have to float safely on the surface by itself without sinking even when pushed slightly under the surface by the boat, a wave or another diver?

I'm interested to see how the two numbers compare.

Later, we can then have a discussion about how easy (or should I say hard ;-) it is to get into (or out of) a set of doubles with fully inflated wing in the water. At least I can share with you my experience.

 

[dannobee]

...Later, we can then have a discussion about how easy (or should I say hard ;-) it is to get into (or out of) a set of doubles with fully inflated wing in the water. At least I can share with you my experience.

Not hard at all. I do it all the time off of my inflatable. Tag off the deco bottles and let them sink, inflate the wing in the doubles, then tag off and throw it in. Jump in, then kit up. No harder than with a singles rig.

 

[Guy Alcala]

Now it starts to make sense to me. Thanks for clarifying. So, I have two more questions then, if you don't mind:

a) How much lift do you think you need if you removed the requirement that the rig needs to float by itself on the surface?

At least 24 lb., and possible 30 or so depending on how much extra I'd want.

b) How much lift does the rig need to have to float safely on the surface by itself without sinking even when pushed slightly under the surface by the boat, a wave or another diver?


I'm interested to see how the two numbers compare.

39+, i.e. the difference in the weight of the gas.

Guy

 

[Joakim Linde]

At least 24 lb., and possible 30 or so depending on how much extra I'd want.

If I may ask, how did you get to 24 lbs? We can always add extra as much as we want to feel comfortable.

My understanding is that you're neutrally buoyant at the end of the dive with no gas in the wing.

 

[David_57]

I'm getting myself geared up to do Fundies in doubles, trying for a tech pass (but not expecting one). I'm probably going to double up my heavy Asahi 100s because I can't afford to get some lighter tanks at the moment. I've been estimating the negative buoyancy of my gear, and it comes out like this:

2 x HP100s -12.5/-10 lb.
Al BP -2 lb.
2 x regs/hoses -5 lb.
bands/crossbar -4 lb.
Can & B.U. lights -3 lb.

Total -39/-24 lb.


I figure I need another 3 lb. or so for my head and a soaked undergarment, or somewhere around 42-45 lb. If I figure that I'll be adding two or three stage/deco bottles once I start tech diving, I probably need 45-50 lb. I'm considering something like the DSS 49 lb. Torus, if I can't find something used. I've asked Rob Lee if he thought that's enough, as I'll likely be taking Fundies from him, or if I should be looking at 55-60 lb. instead. I thought I'd ask it more generally to see what local divers are using, and why. So feel free to recommend what you use/would like.

Thanks,

Guy

I use double HP 100 X7 Worthington's most of the time I have a Luxfer Aluminum 40 for my deco bottle with a OMS 60 LB wing on a stainless back-plate, along with a 4 mil compressed neoprene drysuit with a couple light layers of underwear. I am 6'1" 208 lbs. This setup works perfect for me and trims out very nice with no need for a weight belt as I have my dry-suit and lift bag for backup to my wing, at the end of my dive with min gas left I am almost perfectly neutral in 15ft of water, some tech divers I know use a 40LB wing which seems to work perfect for them.

 

[Guy Alcala]

If I may ask, how did you get to 24 lbs? We can always add extra as much as we want to feel comfortable.

My understanding is that you're neutrally buoyant at the end of the dive with no gas in the wing.

See post #21.

Guy